Flashcards
OCR A-level Physics: Electrons, Waves and Protons
Cards in this deck (32)
- 1What differences are there between e.m.f and p.d?Potential difference is work done per unit charge whereas e.m.f is energy transferred per unit charge.
E.M.F transfers energy from chemical to electrical whereas p.d transfers electrical into other forms of energy. E.g. (sound) - 2How would you find how many charge carriers there are in a given amount of charge?It's the total charge divided by charge on a single electron (elementary charge).
- 3What is current?The rate of flow of charge (A)
- 4State the equation associated with the "mean drift velocity" and state what a high/low value of 'n' would mean.I = Anev
If the number density of charge carriers(n) is high, it implies the material is a good conductor conversely if it is near to zero then it's an insulator. - 5Name the charge carriers in: A - a metal B - an electrolyteA - Electrons
B - Ions - 6Explain Ohm's law?Ohm's law states that for a conductor the p.d is directly proportional as long as all other factors are kept constant, e.g.(temperature).
- 7State the factors that affect resistance?Material - Good conductors will have low resistances due to the high number of delocalized electrons.
Length - Longer lengths of wire will have less current due to more ions opposing the flow resulting in higher resistance.
Cross-sectional area - Wider wires results in a larger current due to more electrons being able to pass a certain point.
Temperature - Higher temperature results in the fixed ions having more kinetic energy making electrons passing through collide more(higher resistance). - 8Identify each I-V graph above.A - Filament Bulb
B - Diode
C - Resistor - 9Describe the difference between resistance and resistivity.Resistivity is an intrinsic property that isn't affected by its dimensions and the value is always the same provided temperature is kept constant whereas resistance can vary depending on a number of factors.
- 10What is power, its unit and the equations associated with it?Power is the rate of energy being transferred with the units Js^-1.
P = VI , P = I²R and P = V²÷R - 11State how you would convert from joules to Kilowatt-hours.Joules -- > KWH = divide by 3.6*10^6
KWH -- > Joules = multiply by 3.6*10^6 - 12Describe Kirchhoff's laws1st - Conservation of charge. Meaning the current entering a junction will be the same when leaving it.
2nd - The sum of the EMF in a closed loop is equal to the product of the resistance and current (in that loop). - 13In a parallel circuit state the general formula for: 1. Resistance 2. Current 3. P.D1. -> 1 ÷ R = 1÷r(1) + 1÷r(2) + 1÷r(n)
2. -> I = I(1) + I(2) + I(n)
3. -> V(1) = V(2) = V(n) - 14In a series circuit state the general formula for the: 1. Resistance 2. Current 3. P.D1. R = R(1) + R(2) + R(n)
2. I = I(1) = I(2) = I(n)
3. V = V(1) + V(2) + V(n) - 15Describe a ______ wave: 1. Longitudinal 2. Transverse 3. Progressive1. Is parallel to the direction of energy transfer and is a series of compressions and rarefactions. E.g. (Seismic waves)
2. Is perpendicular to the direction of energy transfer. E.g (EM waves)
3. Is a wave that transfers energy from a source - 16Explain the difference between Phase and path difference.Phase difference is how far apart two waves are (measured in radians). Path difference on the other hand is the distance between two waves reaching the same point (given meters).
- 17State the equations associated with the speed of a wave?V = λ ÷ T
V = F x λ - 18Define intensity and the equation associated with it.Is the rate of energy transferred in a wave moving from one point to another through space perpendicular to the direction the wave is travelling. (wm^-2)
I = P ÷ A - 19What properties are shared by all Electromagnetic waves?- They can travel through a vacuum
- They all have a magnetic and electric -
- wave interlocked at right angles.
- They're transverse waves
- They can be reflected,diffracted and refracted
- They can all be polarised and experience interference. - 20Describe reflection, refraction and diffraction.Reflection - Is a change in direction of a wavefront in which it meets a boundary between 2 mediums and it stays in the original medium.
Refraction - When a wave meets a boundary and its speed changes within the new medium.
Diffraction - The spreading out of a wave when it meets an obstacle. E.g. (gap) - 21What is polarisation?It is the process of reducing a wave to a single plane commonly done using a polaroid filter.
- 22Define Interference.Is the addition of two or more waves that results in a new wave pattern (superposition).
- 23Give the orders of magnitude of the wavelength of a: -Radio Wave - Light Wave - Gamma WaveRadio = 4 to -1
Light = -7 (micro)
Gamma = -9 to -16 (nano to femto) - 24State Malus' law and the equation associated with it.states that the intensity of a beam of plane-polarized light after passing through a rotatable polarizer varies as the square of the cosine of the angle through which the polarizer is rotated from the position that gives maximum intensity.
- 25How would you find the refractive index of a material?Speed of light in vacuum ÷ Speed of light in the material
- 26Give the equations associated with Snell's lawn₁ x sin(θ)₁= n₂ x sin(θ)₂
or
n x sin(θ) = constant - 27The angles of incidence and refraction are measured to the: A - Boundary line B - Normal lineAnswer = B
- 28Explain the term 'total internal reflection', the conditions required for it to occur and the equation associated with finding the 'critical angle'?Total internal reflection is where a ray instead of being refracted in the new medium it is completely reflected. This occurs when the angle of incidence is greater than the 'critical angle'.
sin(C) = n₂ ÷ n₁ where n₁ > n₂ - 29State the Principle of superposition?If two (or more) waves meet of the same type then the resultant wave can be found by adding the displacements (not amplitudes) of the individual waves.
- 30Explain Coherence.Coherence is when the individual waves that make up the resultant waves have a constant phase difference/frequency.
- 31For constructive and destructive interference to occur the: 1). Path difference must be 2). Phase difference must beConstructive:
1). A multiple of wavelength. E.g.( λ, 2λ)
2). A multiple of 360degrees
Destructive:
1). An Odd number of half wavelengths E.g(½λ)
2). A multiple of 360 degrees /2 - 32—
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- A level Physics Flashcards on OCR A-level Physics: Electrons, Waves and Protons, created by Elliot Smith on 09/08/2017.
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